1. Field of the Invention
The present invention relates generally to radio frequency systems such as radio frequency identification (RFID) systems, and more specifically to RFID transponders having patterned metal used to form an antenna fabricated of a screened conductive paste.
2. Description of Related Art
In the automatic data identification industry, the use of RFID transponders (also known as RFID tags) has grown in prominence as a way to track data regarding an object to which an RFID transponder is affixed. An RFID transponder generally includes a semiconductor integrated circuit having a memory in which information may be stored. An RFID interrogator containing a transmitter-receiver unit is used to query an RFID transponder that may be at a distance from the interrogator. The RFID transponder detects the interrogating signal and transmits a response signal containing encoded data back to the interrogator. RFID systems are used in applications such as inventory management, security access, personnel identification, automotive toll collection, and vehicle identification, to name just a few.
Such RFID systems provide certain advantages over conventional optical indicia recognition systems (e.g., bar code symbols). For example, the RFID transponders have a memory capacity of several kilobytes or more, which is substantially greater than the maximum amount of data that may be contained in a typical one-dimensional bar code symbol. The RFID memory may be re-written with new or additional data, which would not be possible with a printed bar code symbol. Moreover, RFID transponders may be readable at a distance without requiring a direct line-of-sight view by the interrogator, unlike bar code symbols that must be within a direct line-of-sight and which may be entirely unreadable if the symbol is obscured or damaged. An additional advantage of RFID systems is that the interrogator may read several RFID transponders at one time.
Conventional RFID transponders are fabricated using a direct chip attach (DCA) process in which an integrated circuit chip is interconnected on a substrate such as a printed circuit board or an organic flexible substrate such as polyimide or Mylar. The chip is electrically connected to metallic traces formed on the substrate using various techniques, such as wire bonding, tape automated bonding or solder bumping. The metallic traces are generally formed using a photolithographic process in which a desired pattern is selectively etched into a copper layer laminated onto the substrate. Signal delay to and from the chip is thereby minimized because the distance between the chip and the metallic traces of the substrate is kept to a minimum due to the elimination of the chip package and corresponding internal interconnects. The DCA process is a generally cost-effective packaging technique since the chip is assembled directly onto the substrate without enclosing the chip in a separate package; however, the photolithographic process used to form the metallic traces is most expensive part of the process. There is great commercial interest in reducing the cost of RFID transponders to make the technology more price competitive with other automatic data identification technologies, such as bar code symbology.
Accordingly, it would be desirable to provide a more cost-effective process for fabricating RFID transponders. It would be further desirable to provide an alternative way to fabricate metallic traces on a substrate.